Vega
Vega measures sensitivity to IV. Largest at ATM and for long-dated options; shrinks toward zero as expiration approaches. Why 0DTE vega is small in dollars but still meaningful in percent of premium, and what IV crush actually does to a position.
Vega is how the option's price responds to changes in implied volatility. Long options have positive vega; short options have negative. It's the greek that gets less attention than it deserves — until IV moves on a position and the trade behaves nothing like the trader expected.
This article covers what vega measures, how it varies across strikes and time, what IV crush actually does to a position, and why 0DTE vega is small in dollars but still meaningful as a percentage of premium.
The definition
The change in an option's price for a 1-point (1 percentage-point) change in implied volatility, holding everything else constant. Long options have positive vega (rising IV helps them); short options have negative vega. Calls and puts at the same strike share the same vega. Despite the name, vega isn't actually a Greek letter.
A long call with vega 5.00 gains about $5 per share if IV rises by 1 percentage point — say, from 15% to 16%. Multiply by 100 for position dollars: $500 per contract per 1-point IV move.
Vega is the only one of the main greeks that responds to changes in implied volatility (the others respond to the underlying, time, or rate). When traders talk about a position being "long vol" or "short vol," they're usually referring to its vega exposure.
A few mechanical notes:
- Sign convention: positive for long options, negative for short. Long anything = positive vega; short anything = negative.
- Calls and puts at the same strike share vega. Both depend on IV the same way through Black-Scholes.
- Units: typically per 1-percentage-point IV change. Some platforms display per 1.0 vol unit (per 100 percentage points) — you'd then divide by 100 to get the per-1% number. Worth confirming what your platform shows.
The shape of the vega curve
Vega peaks at ATM and falls off symmetrically toward deep ITM and deep OTM. The curve is bell-shaped — the same shape as gamma, with the peak at the strike.
The chart below plots vega as a function of the underlying. Drag the time-to-expiry slider toward zero and watch the entire curve shrink — vega for a near-zero-DTE option is small everywhere.
- Vega (per 1% IV) at $5,000
- $5.69
- Call strike · time
- $5,000 · 30 d
The peak at ATM is for the same structural reason as every other ATM concentration: ATM options have the most extrinsic value, and extrinsic is what IV is pricing. A 1-point change in IV moves the price of an ATM option more than it moves the price of a deep-ITM (which is mostly intrinsic) or far-OTM (which has very little premium to revalue) option of the same expiration.
The shrink toward zero as you drag time down is the article's main 0DTE point — covered below.
How vega scales with time
Vega scales roughly with √T — the same square-root-of-time relationship that governs how extrinsic value scales overall.
For an ATM SPX option around 15% IV (per share):
- 30-day ATM: roughly $5 per share per 1% IV change.
- 7-day ATM: roughly half that.
- 1-day ATM: about a fifth of the 30-day value.
- 0DTE in the final hour: pennies per share.
The exact numbers depend on the strike's IV, the underlying level, and the time remaining; you can verify the relative magnitudes by dragging the time slider on the chart above. The qualitative pattern — vega shrinks fast as expiration approaches — is what matters for position management.
The intuition: vega is the price sensitivity to IV, and IV is the market's pricing of future volatility. As the time horizon over which that volatility can play out shrinks toward zero, IV's relevance to the option's value shrinks with it. By the close, the option is worth exactly its intrinsic value, and IV is irrelevant.
IV crush, briefly
The most-cited vega event in retail options trading is IV crush.
A sharp drop in implied volatility after an anticipated event resolves — earnings for a stock, an FOMC meeting or major macro release for an index. Long options lose value (a negative outcome for them since their vega is positive), even if the underlying moves in the trader's predicted direction. Short options benefit (negative vega meets falling IV).
The mechanics: leading up to an event, IV rises as the market prices in uncertainty. Option prices reflect this elevated IV — they're pricing in a wide range of possible outcomes. After the event resolves and the actual outcome is known, the uncertainty is gone, IV drops back to a normal level, and option prices drop with it.
A common trap. "I bought a call ahead of earnings, the stock went up, but the call lost money." What happened: the call gained from delta on the underlying move, but lost more from IV crush after the announcement. IV that was 60% pre-earnings dropped to 35% post-earnings. The vega loss exceeded the delta gain.
The opposite — IV expansion — helps long options and hurts short. An unexpected sharp move in the underlying often comes with IV expansion as the market re-prices uncertainty. Short-premium positions can get hit twice: by gamma (the underlying moved against them) and by vega (IV expanded against them).
Vega on 0DTE
Vega for a 0DTE option is small in dollar terms. A 1-point IV change might move a $5 0DTE ATM option by a small fraction of a dollar — modest in absolute terms but a meaningful percentage of the premium.
The "small in dollars" framing is technically true but can be misleading. Even $0.20 is 4% of a $5 option's premium — material on a percent basis even though it's a small absolute number. For short-premium trades that collected $5 of credit, a 5-point IV expansion eats roughly $1 of the credit before any underlying move happens.
For 0DTE traders, the main practical consequence is that IV moves intraday remain material on a percentage basis. The morning often sees IV at one level, post-announcement IV at another, and the close at a third. Watching IV across the session — not just at trade entry — is part of reading a 0DTE position.
That said, vega usually isn't the dominant greek on 0DTE. Gamma and theta drive most of the P&L; vega is the supporting actor. But it's not zero, and ignoring it produces surprises on IV-mover days.
Vega in the context of the other greeks
A quick comparison of what each main greek responds to:
| Greek | Responds to |
|---|---|
| Delta | Underlying price |
| Gamma | Underlying price (2nd-order) |
| Theta | Time passing |
| Vega | Implied volatility |
| Rho | Risk-free rate |
Vega is the trader's measure of "how much do I care about volatility itself, as distinct from where the underlying actually goes?" A position can be delta-neutral (no view on direction), gamma-neutral (no view on convexity), and theta-neutral (no view on time), and still have substantial vega exposure — that's a pure vol position.
Most retail strategies don't isolate vega deliberately, but every options position has some. Long options are net long vol; short options are net short vol. Knowing your net vega tells you what an IV move does to your portfolio independent of everything else.
Reading vega from a chain
Vega values you'll typically see on a chain (SPX, ATM, around 15% IV — for non-ATM strikes or different IV regimes, the numbers shift):
- 30-day ATM: a few dollars per share per 1% IV change. Multiply by 100 for position dollars.
- 7-day ATM: roughly half.
- 1-day ATM: about a fifth of the 30-day vega.
- 0DTE ATM in the final hour: pennies per share.
To translate vega to position terms, multiply by contract multiplier (100). A position vega of -$30 means the position loses $30 per 1-point IV expansion — it's net short vol.
Key takeaways
- Vega is the option's price change per 1-point IV move. Positive for long options (they gain when IV rises); negative for short.
- The vega curve is bell-shaped across strikes, peaking at ATM. Same structural reason as gamma and extrinsic value peaking at ATM.
- Vega scales roughly as √T. Long-dated options have meaningful vega; 0DTE vega is small in dollar terms.
- IV crush — a sharp post-event IV drop — is the classic vega event. It can produce losses on long options even when the underlying moved favorably.
- On 0DTE, vega is small in dollars but still material as a percentage of premium. Gamma and theta dominate, but ignoring vega produces surprises on IV-mover days.